1. Field of the Invention
The invention relates generally to the field of mass air flow measurement. More particularly, the invention relates to a housing for a mass air flow sensor used for measuring the mass of a medium flowing in a line, in particular the intake air mass of automobile internal combustion engines.
2. Background of the Invention
Mass air flow sensors are used to measure air intake into an automobile's internal combustion engine in order to optimize fuel delivery to the engine. Specifically, the engine's control module needs to know the intake air volume to calculate the engine load so that it can determine how much fuel to inject, when to ignite the cylinder, and when to shift the transmission. Thus the mass air flow sensor is a critically important sensor for achieving optimal engine control. Without this information, the engine's control module would not know how much fuel to add to the engine.
A mass air flow sensor works by converting the amount of air that it samples from the air drawn into the engine into a voltage signal. Large amounts of air flow into the intake of the engine can cause the sensor to exceed its voltage range. This poses a problem for individuals wishing to increase engine performance by increasing the air flow into the engine's intake manifold. Often individuals desiring increased engine performance replace factory-installed intake manifold components with components that will allow greater air flow to the engine, but the voltage limit of the mass air flow sensor can be a problem, because when the voltage limit of the mass air flow meter is exceeded, the engine's control module will assume that there is something wrong with the engine, and the vehicle's “check engine” light may come on and there may even be damage to the engine, depending upon how the automobile's computer tries to correct the detected off-nominal situation.
One way to configure the mass air flow sensor so that increased air flow in the intake manifold does not exceed the mass air flow sensor's maximum voltage is to lessen the air flow that the sensor experiences while increasing the actual air flow to the engine. As an initial matter, the mass air flow sensor does not experience the full load of air flowing into the intake manifold even in the factory-installed engines. In other words, the sensor is not just sitting in the main air flow path sampling the incoming air. Rather, in most inlet tracts the sensor samples the air flow through a calibrated tube that is part of the mass air flow meter housing and is designed to sample only a portion of the air into the manifold. By changing the calibration tube's size, location and configuration, a user can force a lesser air flow to the mass air flow sensor and therefore “trick” the engine into thinking the flow into the engine is less than it is in reality. The present invention achieves this objective by providing a mass air flow sensor housing that allows increased air flow to the engine while decreasing air flow across the sensor.
Another problem with the operation of mass air flow sensors is that their readings can be affected by reverse flow or back flow of air in the direction opposite of air intake. This back flow often causes inaccurate air flow readings because typical mass air flow sensors detect the flow of the air in both the forward and reverse directions relative to air intake. Prior art mass fluid and air flow devices have attempted to reduce or eliminate back flow. For example, U.S. Pat. No. 4,393,697, entitled “Air Flow Rate Measuring Apparatus,” teaches an air flow rate measuring apparatus having an air flow sensor and a temperature sensor which are disposed in a bypass passage for intake air formed in the vicinity of a main air flow guide chamber in an internal combustion engine. This prior art invention provides protection against back flow in the bypass passage because the air is introduced at right angles into the main passage from the output of the bypass passage. A disadvantage of this invention was that it required a complex mass air flow housing casting that was not inserted into the main air flow path.
U.S. Pat. No. 5,355,726, entitled “Housing for Reducing Back Air Flow to Mass Air Flow Sensors,” reduces back air flow by channeling the sampled air through a “stair-stepped” bypass passage similar to the simplified cross section shown in FIG. 1, which is a prior art mass flow meter housing (from the intake manifold of a 1996-2001 Ford Mustang®). This prior art design successfully reduces back air flow pressure into the calibration tube, but, as can be seen from the simplified cross-section in FIG. 2, the bypass passage's bisecting of the air flow path decreases air flow through the housing and into the intake manifold. FIG. 3 is a simplified cross-section of another prior art mass flow meter housing (from the intake manifold of a 1989-93 Ford Mustang®) showing the reduced air flow area caused by the bypass passage to the mass air flow sensor.
It would be desirable to have mass air flow sensor housing that addresses all of the goals of increasing air flow to the intake manifold for increased engine performance while also decreasing air flow to the mass air flow sensor, and reducing back flow into the calibration tube, all with a simplified casting design.